Coughing is the body's way of getting foreign substances, phlegm and mucus out of the respiratory tract. Coughs are generally useful and preferably not eliminated. However, in many instances, coughs can be severe enough to impair breathing or prevent rest. Water and other liquids, such as fruit juice, have been traditionally used to soothe an irritated throat as a result of severe coughing. Liquids also moisten and thin the mucus in the throat so that it can be coughed up and expelled more easily. The cough suppressant controls or suppresses an irritating or nagging cough as it subdues the body's coughing reflex.